Vacuum casting apparatus

ABSTRACT

A mold core and a mold casting are positioned to define a mold cavity and the melt of the material is drawn into the cavity under vacuum. The vacuum can be eliminated after the melt in the cavity has solidified about the melt entrance openings leading into the cavity or can be maintained to some degree to draw off gases. The resulting casting can be of any shape and, where annular, can be used to make piston rings.

United States Patent 1 1 Iten et al. 1 1 Nov. 27, 1973 54] vAcUUMCASTING APPARATUS 2,082,588 6/1937 Menetrey 1641254 x Inventor: JuliusHeimgarmer Post 2,210,544 8/1940 Galloway 164/119 X 5 Amkom swlilerland.n FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Sulzer Brothers, Ltd.,Winterthur, 644,194 7/1962 Canada 164/306 Switzerland 1,055,764 4/1959Germany 164/306 22 Filed: Mar. 19, 1971 Primary Examiner-J. SpencerOverholser [211 P 126,007 Assistant Examiner-John E. Roethel RelatedU.S. Application Data Division of Ser. No. 820,385, April 30, 1969, 91199 225111,

ForeignAppllcation Priority Data Feb. 28, 1969 Switzerland 3034/69 U.S.Cl 164/255, 164/63, 164/337 Int. Cl B22! 27/16 Field of Search164/113,114,118, 164/119, 61, 63,133,136, 253, 254, 255,

References Cited UNITED STATES PATENTS 10/1948 Higgins 164/114Attorney-Kenyon & Kenyon Reilly 8L Chapin [57] ABSTRACT A mold core anda mold casting are positioned to define a mold cavity and the melt ofthe material is drawn into the cavity under vacuum. The vacuum can beeliminated after the melt in the cavity has solidified about the meltentrance openings leading into the cavity or can be maintained to somedegree to draw off gases. The resulting casting can be of any shape and,where annular, can be used to make piston rings.

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SHEET 5 OF 5 In venfor uuuus HEIMGQRTNER ATTOR EYS VACUUM CASTINGAPPARATUS This application is a division of Ser. No. 820,385 filed Apr.30, 1969, now abandoned.

This invention relates to a method and apparatus for casting of articlesand to the article produced. Still more particularly, this inventionrelates to a method and apparatus for casting a hollow cylindrical blankfor use in making piston rings.

The construction of modern internal combustion engines with elevatedpressures in the cylinders and increased rotational speeds as well asthe adoption of lighter construction methods have greatly increased thestresses imposed on piston rings. Moreover, there is a demand for theuse of piston rings of progressively decreasing material cross-sectionand in particular for piston rings of small height. Accordingly,materials of high static and dynamic strength, high modulus ofelasticity and high impact strength, for example certain mallcable castand spheroidal graphite cast grades are increasingly employed for pistonring materials. In addition, at the present time, it appears to benecessary for the production of high-grade piston rings in most cases toproduce such piston rings by the form turning method from cast blankswhich substantially correspond to the finished ring shape.

The use of the aforementioned new materials as well as the very smallheight often adopted for piston rings leads to difficulties in castingand subsequent treatment of the blanks. Known casting methods for theproduction of piston rings, namely the individual casting methods,centrifugal casting methods and sleeve casting methods no longer meetthe requirements. For example, the individual casting method isunsuitable because, in view of the small material cross-section of thepiston rings to be cast, the metallurgical facilities militate againstthe metallurgical requirements with regard to the sliding and runningcharacteristics of the wear resistance. Moreover, the efficiency of suchmethods is questionable in view of the solidification conditions whichprevail with these methods. A principal disadvantage of the centrifugalcasting method for the production of piston rings is its inability tocast noncircular blanks of the kind frequently required for theproduction of piston rings. Moreover, the machining allowances are largeand not uniform over the entire length of the external circumference.The solidification conditions are also unfavorable in the sleeve castingmethods, where the material is cast in wet or dry sand. Moreover, thismethod requires relatively large machining allowances on the externaland internal sleeve circumference. However, these allowances have notbeen uniform over the entire length of the sleeve and thus rendermanufacture of the pistonrings more expensive. This added expense inalso due in part to the high mechanical strength of modern piston ringmaterials.

Accordingly, it is an object of the invention to provide an economicalmethod of casting blanks for making piston rings.

It is another object of the invention to provide an apparatus forproducing a casting in a relatively simple economical manner.

It is another object of the invention to produce a casting blank whichcan be readily formed into precision piston rings.

lt is another object of the invention to be able to cast modern castingmaterials into hollow shapes with a relative minimum of effort and witha high degree of efficiency.

It is another object of the invention to provide an apparatus for vacuumcasting large castings economically, the filling opening having a largediameter so that the casting material can flow rapidly into the mold.

Briefly, the invention provides a method and apparatus for casting meltsof materials into casting blanks with the use of a vacuum.

The method generally consists in bringing a mold cavity into contactwith a melt through a relative movement between the mold cavity andmelt, in subsequently evacuating the mold cavity so that the melt entersinto and rises within the mold cavity until reaching a predeterminedheight, and in allowing the melt to solidify in the mold cavity. Theevacuation of the mold cavity is maintained at least for as long as isnecessary for the communicating filling passage between the mold cavityand melt to be interrupted by solidified melt material while ahydrostatically sealing means is used to close off the filling passageto a backflow of the melt material from the mold cavity.

The casting produced in accordance with the method may be a hollowcylindrical casting. The casting can be widely employed, either as anindividual product or as a starting product for further processing, forexample for processing into valve seat rings.

The apparatus of the invention includes a chamber which can be evacuatedand which serves as a mold cavity. The chamber is provided with at leastone filling passage for introduction of the melt into the interior ofthe chamber and is otherwise closed. In addition, the apparatus includesmeans for inducing relative motion between the mold and the melt.

In one embodiment of the apparatus, the chamber can be provided with anoutlet for connecting to a suitable vacuum source for evacuation of thechamber interior. In another embodiment, the chamber can be made ofporous material and can be evacuated by a suitable vacuum source throughthe walls of the chamber.

In another embodiment the chamber is formed with a core, a mandrel whichengages the core and a split mold which envelops the core and mandrel soas to define a mold cavity therebetween.

In another embodiment, the chamber can be formed by a mold having aplurality of cores wherein the mold communicates through a sprue withthe melt. In this instance, the mold is placed in a housing in spacedrelation to the walls of the housing and the resulting space isconnected to a vacuum source for evacuation. The mold is either porousto the passage of air and gas or is provided with outlets to communicatethe mold cavity with the housing interior.

In addition, the sprue is provided with any one of a number of varioussealing means to seal off the mold cavity against a back flow of themelt from the cavity prior to solidification. For example, a reversebend or a valve arrangement can be used to block the back flow of melt.

The mold chamber of the apparatus can be filled from the bottom and canremain in a stationary position until solidification takes place or canbe tilted about a horizontal axis after filling so as to prevent leakagewhile solidification takes place. Further, the chamber can be rotatedabout a vertical axis so that the melt can solidify under centrifugalforce against the side walls of the chamber.

These and other objects and advantages of the invention will become moreapparent from the following detailed description and appended claimstaken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a cross sectional view of a casting apparatusaccording to the invention;

FIG. 2 illustrates a view of the riser tube of FIG. 1 after emergingfrom a melt;

FIGS. 3 and 4 each illustrate various embodiments of a sealing meansaccording to the invention;

FIG. 5 illustrates a casting apparatus adapted for rotation according tothe invention; and

FIG. 6 illustrates a further casting apparatus adapted for rotationaccording to the invention.

Referring to FIG. 1, the casting apparatus has a housing 201 with acasting mold 202 incorporated therein. The mold 202 is constructed ofcores 203 of a conventional mold sand or molding compound and isprovided with a riser tube 204 of gas impermeable material whichcommunicates with the mold cavity 222 of the mold 202. The riser tube204 has a refractory lining 205 so that a sprue 206 is formed. The risertube 204 also has a sealing means in the form of an integral U- shapedpart 233 on the lower end of the riser tube 205 to form a communicatingvessel and to extend into the lower end of the sprue 206. The housing201 is hermetically closed with a cover 309 by means of screws 210. Thecover 209 is provided with a suction line 211 which is connected via aflexible hose 212, a regulating valve 213 and a pipe section 214containing a pressure gauge 215 to a vacuum line 216. The vacuum line216 extends into a vacuum source (not shown). The pressure in the vacuumline 216 can be regulated by means of a regulating valve 217 whichcommunicates via a pipe section 218 with atmosphere.

The casting mold 202 is located in the housing 201 by means of aplurality of screws 219 which bear upon a plate 220 so that the mold 202is surrounded by a vacuum chamber 221. In order to enable the vacuumprevailing in the suction line 211 to extend into the mold cavity 222,the plate 220 is constructed of porous, gas permeable material.Alternatively, or in addition, the plate 220 can be provided withapertures 223 for communicating the mold cavity 222 with the vacuumchamber 221.

In use, the casting apparatus is disposed over a melting furnace or aladle 224 containing a melt (casting material) 225. The riser tube 204is immersed in the melt 225 so that the mold cavity 222 is sealed offfrom atmosphere. Next, with the sealing means 207 in the sprue 206 beingopen, the vacuum in the vacuum line 216 is adjusted to a value which,after opening of the valve 213, produces a vacuum in the mold cavity 222which ensures that for a given specific gravity of the casting material,its vapour pressure and prevailing barometric pressure the castingmaterial flows into the casting mold 202 at optimum velocity.

The gases formed from the mold material are drawn off via the suctionline 211 through the plate 220 and through the porous mold material ofthe casting mold 202. After the entire mold cavity 222 is filled withcasting material, the casting mold 202 may then be moved outside theladle zone. When the riser tube 204 emerges after the casting operationfrom the melt (FIG. 2), the casting material is retained in the castingmold by virtue of the atmospheric pressure acting on the castingmaterial level 234 in the section 233a of the U- shaped part 233,provided the vacuum in the casting mold is sufficiently high. Thesealing means thus operates hydrostatically. After closing of the valve213, it is possible for the housing 201 to be opened and the castingmold 202 to be dismantled and for the casting to be removed.

Instead of being constructed of porous materials such as molding sand,the casting mold 202 may also be constructed of solid material, forexample ceramics, steel or a plastic. In order to vent such a moldcavity it is necessary for the cavity to be connected via one or moreventing ducts to the vacuum chamber 221 which surrounds the castingmold. The venting ducts must also be sufficiently small to ensure thatthe casting material entering therein solidifies directly.

Referring to FIG. 3, the sealing means can also be constructed as anautomatic ball valve 235 which is disposed in the sprue 206. The ballvalve 235 has a valve ball 236 which cooperates with a seat cone 237 inthe lining in order to control the flow in the sprue 206. The valve 235is employed in the event that the weight of the ball is greater than itsbuoyancy in the casting material. For example, if the casting materialcomprises aluminium, it is possible for the ball 236 to be constructedof steel. When the casting material rises in the sprue 206 during thecasting operation, the ball 235 is raised as far as a stop 238 so thatthe casting material can enter the mold cavity. On completion of thecasting operation the ball 235 is once again lowered on to the seat cone237 and in this position closes the sprue 206 to prevent the dischargeof casting material.

Referring to FIG. 4, the sealing means can also be formed as a ballvalve 240 having a ball 241 which cooperates with a seat cone 242. Thisvalve 240 is used in the event that the weight of the ball 241 is lessthan its buoyancy in the casting material. This may occur, for example,in the case of a hollow sphere of plastic material and where wax orplastic, for example, Caprolactam, is used as the casting material. Whenthe casting material rises in the sprue duct 206, the ball 241 is movedfrom the seat cone 242 by the casting material and thrust against a stop243 so that the casting material can enter the mold cavity. Aftercompletion of the casting operation, the ball 241 is once again thruston to the seat cone 242 by virtue of the casting material buoyancy thusclosing the sprue duct 206.

The sealing means described hereinbefore are all disposed in or on thesprue of the casting mold. Further, by providing the floor of thecasting mold with the appropriate shape and dimensions, the sealingmeans can alternatively be disposed in the floor itself. For the castingoperation, the casting apparatus is thus lowered in the direction of themelt until the floor immerses to a reliable extent in the melt.

Referring to FIG. 5, a further construction for preventing the dischargeof casting material after emergence of the riser tube from the meltconsists in mounting the casting apparatus for rotation about itslongitudinal axis. To this end, the housing 201 with the casting mold202 disposed therein is supported by a hollow shaft 260 which isjournalled in a bearing 261. A gearwheel 262 in which a pinion 263 of amotor 264 meshes is mounted on the hollow shafl 260. The motor 264imparts rotation to the housing 201 and casting mold about thelongitudinal axis 265 thereof. The stationary suction line 211 of thevacuum apparatus described hereinabove is connected to the hollow shaft260 by means of a gland 266 with a seal 267 so as not to participate inthe rotation. The casting mold in this instance comprises a vessel 268of a porous or solid material. If the casting mold is made of moldingsand, ceramic or the like, either a back filling 269 of sand or steelscrap is provided between the casting mold and the housing 201 or thecasting mold is supported by other mechanical means relative to thehousing 201. The floor 270 of the vessel 268 is provided with anaperture 271 while the top of the vessel 268 is closed with a cover 273which has ducts 272 communicating the mold cavity with the housinginterior.

In order to produce a casting the housing 201 is set into rotation whilethe riser tube 204 is immersed and the suction line 211 is connected tothe vacuum apparatus. The casting material which flows into the moldcavity rises on the internal wall of the mold cavity due to thecentrifugal force and thus forms a cylinder 274 of casting materialthereat. After the casting operation, the vacuum is interrupted, whilethe rotation of the housing 201 is continued. This prevents discharge ofcasting material while the casting apparatus is moved outside the ladlezone in order to allow the next casting operation to commenceimmediately. After the casting material has sufficiently solidified,rotation may also cease.

Alternatively, it may be desirable to maintain the vacuum duringrotation in order to enable any gases which may have developed to bedirectly discharged. During the casting operation, the casting mold neednot be rotated while the casting material is drawn up into the moldsince it is only necessary to set the casting mold into rotation afterthe casting material has reached that level in the mold cavity which isdetermined by the dimensions of the casting. Only then will the castingbe molded.

Although rotation of the casting apparatus in this case serves toprevent the discharge of casting material, it is evident that theapparatus described herein may be employed generally as a centrifugalcasting apparatus. In known centrifugal casting apparatus with avertical centrifuging axis, the casting material is introduced through acasting trough, introduced from above into the casting mold andextending with its discharge end to the center of the casting mold. Bycontrast, the introduction of the casting material into the casting moldby means of suction in the illustrated apparatus (FIG. 12) issubstantially simpler and more economical and is associated with lessturbulence.

Referring to FIG. 6, a rotating casting apparatus can be constructedwithout a housing. For example, the casting mold 280 can be formed as ahollow cylinder 281 which is clamped by means of clamping bolts 282between a supporting plate 283, fixedly joined to the hollow shaft 260of a driving means (not shown), and a removable floor 284. The hollowcylinder 281, the supporting plate 283 and the floor 284 are made of astrong material, for example steel. The supporting plate 283 is providedwith a centering disk 285, for example of ceramic, on which the hollowcylinder 281 is centered relative to the axis of rotation of the castingapparatus. The floor 284 is provided with a riser tube 286 having alining 287 of a material resistant to the prevailing temperature. Thelining 287 is supported by a disk 288 which covers the floor 284 and maybe constructed of the same material as the lining 287. The disk 288 alsoserves to center the hollow cylinder 281.

During use, the casting material is drawn up by a vacuum to pass throughthe sprue 289 in the riser tube 286 and enters the mold cavity 290 andis centrifuged therein to form a cylinder 291. A centering disk 285 ofthe corresponding external diameter and a hollow cylinder 281 ofcorresponding internal diameter is employed depending on the diameter ofthe casting. Adaptation of the casting apparatus to the length of thecasting is made possible without difficulty by the clamping bolts 282.

The invention thus provides a method of producing hollow cylindricalcast blanks which can be used in the manufacture of piston rings withthe piston rings being parted from the blanks. Since the material is notcast into sand, the casting material solidifies rapidly. Accordingly,the material structure of the cast blanks is finer, a feature which inturn increases the mechanical strength of the piston rings. Rapidsolidification also renders the method more economical. This alsoapplies to the fact that the necessary machining allowances are small sothat the subsequent machining work required is small. Piston ringsproduced in accordance with the invention fully meet the demands ofmodern engine construction and of efficient production of high-gradepiston rings. The method is equally suitable for the production ofcircular as well as non-circular, for example oval piston rings. Themold and core can also be constructed of appropriate radialcross-sections for the production of non-circular piston rings.

The casting may be made asymmetrical by employing an asymmetricalcasting mold and/or core mold. Also, by adopting a suitable shape forthe interior wall of the casting mold and/or of the circumferentialsurface of the core, it is possible to construct the circumference orcavity of the cast object as desired.

The method described above is suitable for the casting of articles ofcast iron having spheordial graphite, of malable cast, of mild steel,bronze and other materials. The articles may be heat treated eitherbefore, during or after further processing in known manner in order thatthe material properties adapted to the appropriate requirements may beobtained. The method permits a very rapid casting operation. Further,owing to its simplicity, the method can be adapted without any extensiveeffort for the purposes of automation by means of suitably designedmachines.

The invention further allows the use of a mold with a large fillingopening to permit rapid filling while effectively sealing the mold forcasting purposes. This permits the vacuum casting of large castingseconomically.

What is claimed is:

1. A vacuum casting apparatus comprising a mold chamber having a moldcavity therein,

at least one opening in said chamber communicating said mold cavity withthe exterior of said chamber for introducing a melt of casting materialinto said mold cavity,

a sprue extending from said opening,

means for evacuating said mold cavity to draw the casting materialthrough said opening into said mold cavity,

means for moving said chamber and the melt relative to each other toimmerse said opening in said melt, and

a U-shaped tube disposed in and extending from said sprue to provide asubstantially unhindered rising of the casting material in the moldchamber, said tube further being adapted to hydrostatically prevent aback flow of casting material from said mold cavity after fillingthereof.

2. A vacuum casting apparatus comprising a mold chamber having a moldcavity therein,

at least one opening in said chamber communicating said mold cavity withthe exterior of said chamber for introducing a melt of casting materialinto said mold cavity,

a sprue extending from said opening,

means for evacuating said mold cavity to draw the casting materialthrough said opening into said mold cavity,

means for moving said chamber and the melt relative to each other toimmerse said opening in said melt, and

a ball valve disposed in said sprue to provide a substantiallyunhindered rising of the casting material in the mold chamber, said ballvalve further being adapted to hydrostatically prevent a back flow ofcasting material from said mold cavity after filling bouyancy in thecasting material.

1. A vacuum casting apparatus comprising a mold chamber having a moldcavity therein, at least one opening in said chamber communicating saidmold cavity with the exterior of said chamber for introducing a melt ofcasting material into said mold cavity, a sprue extending from saidopening, means for evacuating said mold cavity to draw the castingmaterial through said opening into said mold cavity, means for movingsaid chamber and the melt relative to each other to immerse said openingin said melt, and a U-shaped tube disposed in and extending from saidsprue to provide a substantially unhindered rising of the castingmaterial in the mold chamber, said tube further being adapted tohydrostatically prevent a back flow of casting material from said moldcavity after filling thereof.
 2. A vacuum casting apparatus comprising amold chamber having a mold cavity therein, at least one opening in saidchamber communicating said mold cavity with the exterior of said chamberfor introducing a melt of casting material into said mold cavity, asprue extending from said opening, means for evacuating said mold cavityto draw the casting material through said opening into said mold cavity,means for moving said chamber and the melt relative to each other toimmerse said opening in said melt, and a ball valve disposed in saidsprue to provide a substantially unhindered rising of the castingmaterial in the mold chamber, said ball valve further being adapted tohydrostatically prevent a back flow of casting material from said moldcavity after filling thereof.
 3. A casting apparatus as set forth inclaim 2 wherein said ball valve includes a seat and a ball located abovesaid seat and being of a weight greater than its bouyancy in the castingmaterial.
 4. A casting apparatus as set forth in claim 2 wherein saidball valve includes a seat and a ball located below said seat and beingof a weight less than its bouyancy in the casting material.